A channel emulator is used to simulate channel effects that radio signals will undergo when propagating across a communication channel. The communication channel can be a wired or wireless communication channel. For a wireless communication channel, the channel effects are one of the most important factors to be considered when designing and implementing the communication channel.
For a radio channel, its radio propagation parameters are constantly changing and are influenced by a number of factors including, for example, location, temperature, the presence of interfering signals, the topography of the surrounding environment, etc. Because of the constantly changing channel parameters, it is difficult to develop a channel emulator that can repeat the same test under the same conditions in a real radio propagation environment. For system performance testing, a controllable channel emulator, which can accurately simulate radio propagation parameters, is highly desired.
For any particular wireless communication standard, specific channel models are used to conduct the performance testing of the wireless communication system which is designed to operate following the same standard. For a real-time test, a channel emulator, which can realize that standard in real-time, is used to perform the system performance and conformance test. Since a channel emulator is an important tool for testing the performance of a communication channel, it is important to have the ability to verify the accuracy and validity of the channel emulator.
When a radio signal propagates over the air, the signal will undergo many effects, such as multipath impairment, large and small scale fading, and other channel impairments which can change over time, location, etc. For example, multipath impairment causes a radio signal to appear as if it traverses different paths, which induces different path delay and pass loss for each path. A channel emulator attempts to simulate all of these channel impairments in order to simulate actual signal propagation parameters. The channel emulator develops what is referred to as a “faded signal” that is intended to represent a signal that has traversed a communication channel having one or more of the above-mentioned impairments. The performance of the channel emulator is based on statistics of communication channel models.
The influence of the channel impairments on the faded signal should be evaluated as a whole when evaluating the performance of a channel emulator. Performance testing a channel emulator is challenging based on a number of factors. Most importantly, there are no well-accepted standard performance metrics or methods to evaluate the performance of a channel emulator. For example, the faded signal provided by the channel emulator changes over time following one or more statistical models, making it difficult to directly measure the faded signal. For example, multiple path fading will result in the spectrum changing over time. There is no straightforward way to evaluate whether such a change is properly represented by the faded signal provided by the channel emulator.
Therefore, it is desirable to have a simple and accurate way to verify the accuracy and validity of the performance of a channel emulator.